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Calculation of excited-state properties using general coupled-cluster and configuration-interaction models
1Institut für Physikalische Chemie, Universität Mainz, D-55099 Mainz, Germany. kallay@uni-mainz.de
The Journal of Chemical Physics
|November 13, 2004
Summary
This study presents new computational methods for calculating excited states in molecules using coupled-cluster theory. These advancements enable more accurate predictions of molecular behavior and chemical reactions.
Area of Science:
- Quantum Chemistry
- Computational Chemistry
- Theoretical Chemistry
Background:
- Accurate calculation of excited states is crucial for understanding photochemistry and spectroscopy.
- Existing methods for excited-state calculations can be computationally demanding and limited in scope.
Purpose of the Study:
- To implement string-based algorithms for calculating excitation energies and analytic first derivatives for excited states within coupled-cluster (CC) linear-response (LR) theory.
- To extend these methods to include transition moments between ground and excited states.
- To provide a versatile framework applicable to various CC wave function types and excitation manifolds.
Main Methods:
- Implementation of string-based algorithms for coupled-cluster linear-response (CC-LR) theory.
- Equivalence of CC-LR and equation-of-motion coupled-cluster (EOM-CC) approaches for excitation energies and first derivatives.
- Application to both single-reference and multireference CC wave functions.
- Comparison with configuration-interaction (CI) methods.
- Benchmark calculations on NH(2) and NH(3) to assess the effect of higher excitations.
- High-accuracy calculations of stationary points on the S(1) surface of acetylene.
Main Results:
- Successful implementation of excitation energies and analytic first derivatives for excited states using CC-LR/EOM-CC methods.
- Demonstration of the applicability to diverse CC wave function types.
- Quantification of the impact of higher excitations on excited-state properties through benchmark calculations.
- Characterization of stationary points on the S(1) surface of acetylene with high accuracy.
Conclusions:
- The developed string-based algorithms provide a robust and accurate framework for excited-state calculations in quantum chemistry.
- These methods offer significant improvements for studying molecular excited states, with implications for spectroscopy and reaction dynamics.
- The study successfully applies these advanced computational tools to a challenging chemical system, acetylene.